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How to Troubleshoot a Heater Blowing Cold Air


If your heater is blowing cold air instead of the cozy warmth you expected, something is wrong. We have compiled a list of possible causes that any homeowner can investigate before calling the HVAC repair company. Most of the time, one of these aspects is the culprit.


The Fans Are Switched Off


It is common practice to switch off the heater’s fans during the summer – it reduces the noise in the ducts but means that the air is not forced into the rooms. Check that the fans are set to “automatic”, and they should come on after a minute or three. If not, switch them to “on” to test if the fans are indeed functioning. Either result – coming on or staying off – will require a more thorough check of the HVAC system by a qualified technician.


Clogged Air Filter


The air drawn into the heater unit is first filtered to remove contaminants. If you don’t clean this filter regularly, it will become so clogged with pollutants that it will no longer let air through. The solution is to replace the dirty filter with a new one made for your heater unit. You should notice the result instantly unless there is something else wrong with the system, which you should never discount as a possibility.


The Thermostat Setting


You set the thermostat to warm, but cold air came out. It always pays to double-check the setting, especially right after performing any of the other troubleshooting tasks. A common reason for changes in the setting is that other people in the house may have turned down the heat. The newer digital touch panels are also susceptible to inadvertent setting changes when finding feedback on the heater’s health.


Continuous Energy Supply


Check that the gas is turned on and available for the heater to use as an energy source. If not, the cause could be that the gas company has temporarily turned off the supply to the neighborhood due to technical difficulties. If this is the case, a quick call to them will provide the necessary information.


For an electric unit, check that the breaker has not tripped. If it has, reset the breaker and try the heater again. If the breaker trips again, leave it off and call the HVAC technicians. Some newer gas units use an electronic pilot light to ignite the gas in the heater. This circuitry, the fans and other electrical components of the heater can cause the breaker to trip.


An Extinguished Pilot Light


An interruption in the gas supply is a common cause for the pilot light to go out. Always follow the instructions in the owner’s manual of the heater to relight the pilot light. However, if the light keeps going out, even though there is a steady supply of gas, something is wrong, and you should call the HVAC technician.


A Dirty Flame Sensor


The purpose of the flame sensor in a gas heater is to determine whether the gas is being burnt or not. It is a very simple yet effective safety feature. If the sensor is dirty, it will not sense the flame, and the gas valve will automatically close.


If you turn the heater off and then on, and hot air briefly comes out and then goes cold, the flame sensor might be causing the problem. The cleaning or replacement of the flame sensor rod is a job for the experienced HVAC technician and should never be attempted by the homeowner.


Patience and Impatience


Another cause of cold air flowing from the heater could be impatience. If the heater is small, located far from the room, and the ambient temperature near-freezing – as an extreme example – the hot air will take a while to reach the room. Modern HVAC systems have many safety features built-in, so it is rarely a risk to let the system run for ten or so minutes to see if the air becomes warm. If this is the cause, we advise you to have the system evaluated by a certified HVAC technician and installer, as it is evident that the heater’s capacity is being overloaded and that it should perhaps be replaced with a larger unit.


Severe Heat Pump Issues


Non-gas burning heaters employ a heat pump. It operates on the principle of exchanging energy to raise or lower the temperature. The units typically have a module on the outside of the house and are thus susceptible to influences like the buildup of snow or nesting mice. Clearing these obstructions are easy for the homeowner to do. However, other problems with the heat pump might include low refrigerant, bad valves or faulty meters. Only an HVAC technician can confirm this.


If none of these troubleshooting tips resolves your heater blowing cold air issue, you should immediately contact an HVAC technician.